The overall objective is to define and study factors associated with the in vivo survival of Rous sarcomas and allogeneic cells in chickens possessing lymphoid cells capable of destroying them in vitro. The major strategem of our anaysis is the use of inbred lines of chickens of known histocompatibility genotype which are agammaglobulinemic (a gamma) or deficient in T-cell mediated immune responses. The subobjectives which describe our approach are: a) to study serum blocking factors in normal and a gamma birds and to establish their relationship to cellular immunity and behavior of tumor in vivo; b) to establish immunological methods for detection of blocking factors and for analysis of their mode of action; c) to determine the efficacy of immunoabsorbents to deplete serum of blocking factors; and d) to identify the effector lymphoid cell. Correlative studies to be performed in allogeneic tolerance will emphasize a) an analysis of blocking factors in a gamma birds with complete or partial tolerance, b) the effect of blocking factor depletion on skin graft survival and cellular chimerism and c) identification of effector cell. Methods to be used include a) in vitro and in vivo assessment of cell mediated immunity, b) development and use of rabbit antibodies to blocking factors and c) use of immunoabsorbents for absorption of blocking factors ex vivo.